Sheet-guiding suction box

ABSTRACT

A sheet-guiding suction box can be adapted to the size or format of a plurality of sizes of sheets to be guided. This is accomplished by structuring the guide box with a plurality of independently acting suction chambers. A central suction area of the guide surface of the suction box is smaller in size than the smallest format of a sheet to be guided.

FIELD OF THE INVENTION

The present invention relates to a suction box for guiding sheets. Thissuction box has a plurality of individually acting suction chambers. Acentral one of these is smaller than the smallest sheet to be guided andis comprised of two individual chambers.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 2,572,640 describes a suction box for holding films in acentral suction chamber, whose extension is less than the smallestformat of a film to be held.

It is disadvantageous in connection with this suction chamber that thevacuum collapses in case of a partial coverage, such as occurs inparticular in connection with moving sheets, so that the dependablesuction of the moved sheet is not assured.

SUMMARY OF THE INVENTION

It is object of the present invention to produce a suction box forguiding sheets.

This object is attained in accordance with the invention by theprovision of a suction box that is used to guide a variety of sizes ofsheets. The suction box is formed having a plurality of independentlyacting suction chambers. At least one central suction chamber isarranged so that its extension is less than the smallest size of a sheetto be guided. Two independently acting suction chambers form thiscentral suction chamber.

The suction box in accordance with the present invention can be adapted,in an advantageous manner, to the format of various sized sheets. Theeffects of secondary air are prevented by this, and an even suctionforce is achieved, even with formats of different size. With largeformats, corners and edges have a greater tendency to flutter. Toprevent the fluttering of corners, suction chambers which can beindependently controlled are provided there.

It is particularly advantageous to employ this suction box in connectionwith inspection systems, because it is necessary, in connection withinspection systems, to guide sheets to be inspected steadily andflutter-free at least during the image recording. This is not absolutelynecessary in remaining areas of a sheet transport path, so that theincreased technical outlay for flutter-free guidance can be avoided.

It is possible by means of an integrated sensor, which is displaceablein the transport direction, to trigger the image recording, in such away that during the recording the sheet is centered in relation to a CCDarea camera of the inspection system.

BRIEF DESCRIPTION OF THE DRAWINGS

The device of the present invention is represented in the drawings andwill be described in greater detail in what follows.

Shown are in:

FIG. 1, a schematic lateral view of a device for the qualitativeassessment of printed sheets,

FIG. 2, a schematic plan view of a device for the qualitative assessmentin the transporting direction of the printed sheets,

FIG. 3, a schematic view from above on a suction box of the device forthe qualitative assessment of printed sheets,

FIG. 4, a perspective plan view of the device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A device for the qualitative assessment of processed material 1 is shownin FIG. 1 essentially consists of a material guide 2, an illuminatingdevice 3, at least one sensor 4 and a downstream connected evaluationdevice.

This quality control system can be employed for monitoring of processedmaterials such as both webs and sheets 1 in a rotary printing press or amachine for further processing. In the present preferred embodiment, thequality control system is employed in a sheet-fed rotary printing pressfor the qualitive assessment of processed materials such as stocks andbonds, and in particular, for banknotes.

For example, sheets 1 to be inspected are conveyed by means of grippersystems 6 on a sheet transport level 7. These gripper systems 6 arefastened to circulating chains 8 of a chain conveyor, which is known perse. The material guide 2 is arranged above the sheet transport level 7.This guide 2 has a shape which, for example, is curved in the transportdirection T on its guide surface 9 facing the sheets 1. This guidesurface 9 therefore is concavely curved in the transport direction T andhas a radius of curvature R9, for example R9=800 mm. The material guide2 is embodied as a suction box 2, for example. To this, end the guidesurface 9 is provided with a plurality of perforations 11, i.e. theguide surface 9 is constituted by a perforated plate as seen in FIG. 3.The perforations 11 each may have a diameter of 2 mm, for example, andmay be spaced from each other in a grid at a distance of 3 mm. Thisguide surface 9 is arranged to be interchangeable with other guidesurfaces having different perforations and can be folded down formaintenance work.

Separating walls are arranged inside the suction box 2, so that a numberof suction chambers 12, 13; 14, 16, 17, 18; and 19, 21, 22, 23 areformed, which acts independently and which are separately controllable.An area in the center of the suction box 2 which approximatelycorresponds to the smallest format of the sheets 1 to be guided isdivided in the transport direction T into a front central suctionchamber 12 and a rear central suction chamber 13. Respectiveintermediate suction chambers 14, 16, 17, 18 adjoin the four sides ofthis central rectangular area 12, 13. Again, four peripheral suctionchambers 19, 21, 22, 23 are arranged next to exemplary of theseinterchangeable suction chambers 14, 16, 17, 18 in the direction ofoutside edges of the sheet 1. The outermost suction chambers 21, 23extending in the transport direction T can be once again be divided.

A vacuum in each of the individual suction chambers 12, 13; 14, 16, 17,18; and 19, 21, 22, 23 can be individually controlled, for example bymeans of a bypass control. In this way, it is possible to adapt aholding force acting on the sheets 1 to the format, material or type ofprocessing of the sheets, for example.

The illuminating device 3 and the sensor 4 are arranged opposite thesuction box 2. The illuminating device 3 has a V-shaped cross section inthe transport direction T, as seen most clearly in FIGS. 2 and 4 i.e. itis designed as a V-shaped box 24. This box 24 has two legs 26, 27 withlevel light outlet surfaces 28, 29 facing the sheets to be inspected.These legs 26, 27 include an opening angle alpha of, for example, 122°.This opening angle alpha preferably has a range between 90° to 150°.Each one of the two light outlet surfaces 28, 29 is shaped generallytrapezoidally as shown in FIG. 1. Here the shorter ones of the two basesides of each of the two trapezoidally shaped light outlet surfaces 28and 29 meet and extend parallel in respect to the transport direction T.The two short base sides each have a length 131 of, for example 350 mm.The two larger base sides 32 each have a length 132, for example 132=560mm, also extend parallel in the transport direction T and are spacedapart transversely to the transport direction T at a distance a32, forexample a32=1220 mm, which corresponds to a width b3 of the illuminatingdevice. This distance a32 is greater than a greatest width b1, forexample 840 mm, of the sheets 1 to be inspected.

Thus, the size and format of the illuminating device is matched to theformat of the sheets 1 to be inspected. The light outlet surfaces 28, 29consist of panes of frosted glass, for example. A plurality of diffuselyradiating light sources have been respectively arranged underneath thesefrosted glass panels. These light sources are embodied as singleflashtubes, for example. A particularly even illumination of the sheets1 to be inspected is achieved by this arrangement of light sources andfrosted glass panes.

In place of the V-shaped cross section, the illuminating device 3 canalso have a curved cross section, for example in the shape of an arc ofa circle.

A plurality of guide strips 33 or shutters extending parallel in thetransport direction T can, and also be placed on the frosted glasspanel. These guide strips 33 are seen in FIGS. 1 and 4 and can be madeof sheet metal or also of frosted glass, for example. An angle ofinclination of these guide strips 33 in respect to the light outletsurfaces 28, 29, or respectively the sheet transport level 7 is matchedto extend parallel with a light beam, wherein such a light beam directedbetween two guide strips 33 impinges on the sensor 4 after having beenreflected on a reflecting area of the sheet 1.

These guide strips 33 have a distance a33, for example a33=20 mm, fromeach other.

The illuminating device can also consist of several, singly arrangedlight sources.

The sensor 4 is arranged in the center of this illuminating device 3. Inthis case, a CCD area camera 4 with a lens fixed in front of it isprovided as the sensor 4. In the present embodiment the lens has beendesigned in such a way that the entire sheet 1 to be inspected iscovered, i.e. a distance between the CCD area camera 4 and the sheettransport level 7 is adapted to the lens of the CCD area camera.However, it is also possible to cover several portions individually oneafter the other and to combine them into a whole image. The sheet 1 tobe inspected is located in the optical axis of the objective of the CCDarea camera 4.

In the present embodiment a sensor, not represented, which acts as atrigger, has been installed in the suction box. This sensor detects thefront edge of the sheet 1 to be inspected and triggers the inspectionprocess. This sensor is arranged displaceably in the transport directionT in order to align the position of the sheet in case of sheet formatsof different sizes in such a way that the inspection takes placeapproximately centered in respect to the lens of the CCD area camera 4.

An evaluation device is connected downstream of the CCD area camera 4.

An image of the sheet 1 to be inspected is divided into a matrixconsisting of a multitude of small image elements, i.e. pixels. Each oneof these pixels is assigned a defined position by providing itscoordinates in the X and Y direction of a Cartesian coordinate system.In-addition, a value Z is assigned to its remission value, for exampleits gray scale value, which defines the latter. Each pixel P_(i) (X_(i),Y_(i), Z_(i)) is therefore exactly defined in its position and size bythe statement of the values X_(i), Y_(i), Z_(i).

The light reflected from the sheet 1 to the individual pixels P_(i) isconverted, corresponding to its strength, by the CCD area camera 4 intoan electrical analog signal. This analog signal is supplied to an A/Dconverter, which forms the digital values Z_(i) from this. Customarily,and the value range is here divided into 0 to 255 discrete values. Inthis case, the value 0 means no reflection at all impinging on thecorresponding pixel P_(i) of the CCD area camera 4, while 255corresponds to a maximum reflection.

In the case of the present application, the sheet 1 to be inspected hasreflecting surfaces. In this connection, “reflecting” is understood tomean that light beams impinging on the surfaces are reflected withlittle scattering and have a noticeably directed portion. Such surfacescan be silver threads in bank notes in particular, or holograms orkinegrams. These reflecting surfaces are to be recognized as such.

A value range is now assigned to the values of the pixels P_(i) of sucha sheet 1 in such a way that the occurring value range outside of thereflecting surfaces clearly lies within the limits 0 to 255. In actualuse, for example, the color “white” is assigned a value Z_(i) from 180to 200, and the color “black” a value Z_(i) between 10 and 30.

This assignment is performed, for example, by means of adjusting thebrightness of the illuminating device 3, the amplification of the camerasignal in the electronic evaluation device, or by the use of a shutterof the lens of the CCD area camera 4.

The sheet 1 is evenly illuminated by means of the illuminating device 3in such a way that each reflecting surface located at any arbitraryplace on the sheet 1, which has almost ideal reflective properties,reflects an incident light beam directly into the CCD area camera 4. Atleast partially directed light beams are used for this. The associatedvalue Z_(i) of a pixel P_(i) assumes a value upon reflection, whichclearly differs from a value assigned to the color “white”. For example,in that case the value Z_(i) of a pixel P_(i) assigned to a reflectingsurface then reaches 230 to 255.

In this way, and areas with reflecting surfaces are clearly defined bymeans of the association of extreme values Z_(i), i.e. area which weaklyscatter and which thus are provided with clearly directed reflectiveportions are differentiated from areas with diffuse reflection.

The pixels assigned to the reflecting surfaces are then recognized assuch by the electronic evaluation device and are further processedaccordingly.

While a preferred embodiment of a sheet-guiding suction box inaccordance with the present invention has been set forth fully andcompletely hereinabove, it will be apparent to one of skill in the artthat a number of changes in, for example the type of press used toaccomplish the printing of the sheets, the source of supply of thesuction to the suction box and the like could be made without departingfrom the true spirit and scope of the present invention which isaccordingly to be limited only by the following claims.

What is claimed is:
 1. A guide for sheets comprising: a suction box; aplurality of independently acting suction chambers in said suction box,said plurality of independently acting suction chambers including twocentral suction chambers, and defining a guided surface, said guidesurface being curved in a transport direction of sheets to be guided; acentral suction area of said plurality of independantly acting suctionchambers, said central suction area being formed by said two centralsuction chambers of said plurality of independantly acting suctionchambers and having a length less than a smallest sheet to be guided;and an inspection system for qualitative assessment of sheets to beguided, said suction box being located opposed to said inspectionsystem.
 2. The suction box of claim 1 further comprising at least firstand second peripheral suction chambers bounding said two central suctionchambers of said plurality of independantly acting suction chambers. 3.The suction box of claim 2 wherein said first and second peripheralsuction chambers extend in the transport direction of sheets to beguided.
 4. The suction box of claim 2 wherein said first and secondperipheral suction chambers extend transverse to the direction oftransport of sheets to be guided.
 5. The suction box of claim 1 furtherincluding means for controlling a suction supply to each of saidplurality of independently acting suction chambers.
 6. The suction boxof claim 1 wherein said guide surface is interchangeable.
 7. A guide forsheets comprising: a suction box; a plurality of independantly actingsuction chambers in said suction box, said plurality of independantlyacting suction chambers including two central suction chambers anddefining a guide surface, said guide surface being curved in a transportdirection of sheets to be guided; and a central suction area of saidplurality of independantly acting suction chambers, said central suctionarea being formed by said two central suction chambers of said pluralityof independantly acting suction chambers and having a length less than asmallest sheet to be guided.
 8. A guide for sheets comprising: a suctionbox; a plurality of independantly acting suction chambers in saidsuction box, said plurality of independantly acting suction chambersincluding two central suction chambers and defining a guide surface; acentral suction area of said plurality of independantly acting suctionchambers, said central suction area being formed by said two centralsuction chambers of said plurality of independantly acting suctionchambers and having a length less than a smallest sheet to be guided;and an inspection system for qualitative assessment of sheets to beguided, said suction box being located opposed to said inspectionsystem.